Published in "Polar Biology 32(9): 1275-1286, 2009" which should be cited to refer to this work. Status of the endangered ivory gull, Pagophila eburnea, in Greenland Olivier Gilg · David Boertmann · Flemming Merkel · Adrian Aebischer · Brigitte Sabard Abstract The ivory gull, a rare high-Arctic species whose >2,000 pairs) since all colonies have not yet been discov- main habitat throughout the year is sea ice, is currently ered and since only 50% or less of the breeding birds are listed in Greenland as ‘Vulnerable’, and as ‘Endangered’ in usually present in the colonies at the time the censuses take Canada, where the population declined by 80% in 20 years. place. Although this estimate is four to eight times higher Despite this great concern, the status of the species in than that previously arrived at, the species seems to be Greenland has been largely unknown as it breeds in remote declining in the south of its Greenland breeding range, areas and in colonies for which population data has rarely, while in North Greenland the trends are unclear and unpre- if at all, been collected. Combining bibliographical dictable, calling for increased monitoring eVorts. research, land surveys, aerial surveys and satellite tracking, we were able to identify 35 breeding sites, including 20 Keywords Pagophila eburnea · Greenland · new ones, in North and East Greenland. Most colonies are Endangered species · Satellite tracking · Climate change · found in North Greenland and the largest are located on Sea-ice islands and lowlands. The current best estimate for the size of the Greenland population is approx. 1,800 breeding birds, but the real Wgure is probably >4,000 adult birds (i.e. Introduction The ivory gull (Pagophila eburnea) is one of the most http://doc.rero.ch O. Gilg (&) remote and poorly known breeding birds in the northern Division of Population Biology, hemisphere. Over its entire breeding range (Canadian Arc- Department of Biological and Environmental Sciences, tic, Greenland, Svalbard and Russian Arctic islands), it University of Helsinki, P.O. Box 65, 00014 Helsinki, Finland breeds either on inland cliVs and ‘nunataks’, i.e. rocky out- e-mail: [email protected] crops emerging from icecaps, or on high-Arctic barren O. Gilg · A. Aebischer · B. Sabard islands or Xatlands. The size of its entire circumpolar popu- Groupe de Recherche en Ecologie Arctique, lation is believed to range between just 8,000 and 11,500 16 rue de Vernot, 21440 Francheville, France breeding pairs (Gilchrist et al. 2008). D. Boertmann · F. Merkel Because the ivory gull spends most of its life cycle on Department of Arctic Environment, sea ice, a habitat that is currently shrinking during the sum- National Environmental Research Institute, mer season (Gascard 2008; Holland et al. 2006; Perovich Aarhus University, P.O. Box 358, 4000 Roskilde, Denmark and Richter-Menge 2009), the species could soon face a F. Merkel dramatic decline, at least in some parts of its breeding Greenland Institute of Natural Resources, range. In Canada, where the status of the species has P.O. Box 570, 3900 Nuuk, Greenland recently been updated to ‘Endangered’, recent studies claim that 80% of the breeding population has already been lost A. Aebischer Musée d’histoire naturelle Fribourg, during the past 20 years (Gilchrist and Mallory 2005). Chemin du Musée 6, 1700 Fribourg, Switzerland Although its status is still under evaluation in all other 1 countries holding breeding populations, this alarming situa- dant, appeared to be visitors from other colonies (Gilg et al. tion has drawn wide attention to the species (Krajick 2003) unpublished), satellite tracking also rapidly appeared to and an international circumpolar ‘Conservation Strategy have great potential to locate new colonies or to conWrm and Action Plan’ has recently been presented by leading occupation of known colonies (all tracked birds were adults seabird experts of the Arctic countries (Gilchrist et al. with incubation patches). To assess this assumption, we 2008). Despite that Greenland, where the species is consid- Wrst listed all inland sites that had been visited more than ered ‘Vulnerable’ (Boertmann 2008a), is believed to hold a ten times within a time period of more than 20 days by a signiWcant part of the world population of the ivory gull, single bird during the breeding season (between 1 July and published data are sparse for the country. The data only 15 August 2007, and 15 June and 1 August 2008). Eight of refer to a limited number of colonies and, with a few excep- the 11 resulting ‘suspected breeding sites’ could be checked tions, have not been updated since the colonies were Wrst by one of us (DB) during aerial surveys conducted between described. 30 July and 1 August 2008, i.e. during the chick rearing The main aims of our study, based on a review of pub- period (see below) in order to (1) validate the method, and lished sources, extensive recent survey from 2003 to 2008 (2) eventually estimate the size of the occupied colonies. as well as coupled satellite monitoring and aerial surveys, Direct surveys, on land or from the air, have been under- were, therefore: taken by the authors since 2003 in order to assess site Wdel- ity and population size at most of the known breeding sites. • to complete and compile the mapping of Greenland All but a few of the breeding sites known for Greenland breeding sites of ivory gull to improve future monitoring could be visited during the course of the two summers, and conservation of these sites 2007–2008, alone. Most of them had not been revisited • to estimate the size of the breeding population of ivory since their discovery. Several new colonies were also found gull in Greenland to update its numerical contribution to during our aerial surveys, both in south-east Greenland and the world population and to assess past or future in North Greenland. changes. In addition to these three main sources of information, we also located three new colonies (two ascertained and one suspected) by inquiring with individuals (i.e. geolo- Materials and methods gists, geographers or mountaineers) that we knew had vis- ited the poorly known nunatak areas of East Greenland Data used in this paper have three main origins: published (68–70°N). sources, coupled satellite tracking and aerial surveys, and Colony sizes given in the results section relate to the direct surveys (land and aerial). ‘highest number of adult birds seen’ at the colonies from Published data are few and far between. They are easy to 1998–2008, or from 1978–2008 if no census data were locate since most biological expeditions investigating the available for the period 1998–2008. Greenland bird fauna often used to publish a summary of http://doc.rero.ch their Weld observations in the Danish Ornithological Jour- nal: ‘Dansk Ornithologisk Forenings Tidsskrift’. Further- more, several syntheses have already summarized past Results studies (Boertmann 1994; Falk et al. 1997; Gilg et al. 2003; Salomonsen 1950, 1961), and the ‘Greenland seabird data- Breeding sites base’ maintained by the National Environmental Research Institute (NERI) in Denmark also aims to maintain updated Altogether, 35 breeding sites are currently (i.e. since 1978) information on all seabird breeding sites known in Green- known in south-east (n = 6), north-east (n = 1) and North land (see, e.g. Boertmann 2008b). Greenland (n = 28; Table 1; Fig. 1). With the exception of Satellite tracking was initiated on ivory gulls in North three sites discovered in 1908 (Renskaeret; Manniche Greenland in 2007 (Gilg et al. 2008a, 2008b) in two of the 1910), 1910 (Nakkehoved; Mikkelsen 1913; Salomonsen largest breeding colonies known in the country (i.e. Station 1967) and 1961 (Station Nord; Salomonsen 1961), all these Nord and Henrik Krøyer Holme; Table 1; Fig. 1). A total of sites have been discovered recently (¸1978) and from a 13 and 5 birds were Wtted with satellite transmitters in 2007 limited number of expeditions (Bennike and Higgins 1989; and 2008, respectively. The primary aim of this study was Bennike and Kelly 1986; Falk et al. 1997; Gilg et al. 2003; to document movements, phenology and site Wdelity of the Håkansson et al. 1981; Hjort et al. 1988; Hjort et al. 1983; species. However, since most birds tagged at Station Nord, Wright and Matthews 1980; present study). The majority of where anthropogenic food supplies (i.e. organic wastes these sites (n = 20) are presented here for the Wrst time from the station’s kitchen and leftover dog food) are abun- (Fig. 1: blue circles). 2 Fig. 1 New (dark dots) and for- merly known (light dots) breed- ing sites of the ivory gull in Greenland and North Greenland (the latest region is detailed in upper panel). Dot size propor- tional to colony size (see legend box; uncounted sites included in the smallest class). Numbers on the map refer to colony descrip- tions in Table 1. Historical and unconWrmed breeding sites (see Table 1) are marked with dark and light stars, respectively http://doc.rero.ch Three additional breeding sites have also been reported at altitudes ranging from 1,500 to 2,500 m a.s.l. (site # 35 is at in north-west Greenland in the past (1854–1922; Bessels approx. 1,150 m a.s.l.). On the other hand, all colonies found 1879; Salomonsen 1950) and six other sites are worth men- in North Greenland (sites # 1–28) are on islands, coastal low- tioning as possible breeding sites (Table 1; Fig. 1). lands, small cliVs or on much lower nunataks (maximum alti- All but one of the six breeding sites found in south-east tude: 1,000 m a.s.l.; all but two sites below 500 m a.s.l.).